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  Electroluminescent device with high refractive index and uv-resistant encapsulantUSPTO Application #: 20070295968Title: Electroluminescent device with high refractive index and uv-resistant encapsulant Abstract: An encapsulant containing nanoparticles that improve the heat and UV resistance properties of electroluminescent devices. The nanoparticles that are suspended in the encapsulant may be either oxides or non-oxides and may include SiO2, TiO2, Al2O3, ZrO2, Ti, TiB2, TiC, and TiN. The nanoparticles may range in size from 5 to 165 nm in diameter. The encapsulant containing nanoparticles may be used in an electroluminescent device by being deposited in a concave base cavity to cover a light source, such as a light-emitting diode (“LED”), positioned in the concave base cavity, and may also be applied in the form of a conformal coating that covers the light source. An electroluminescent device utilizing the encapsulant containing nanoparticles and a method of producing such a device is also provided. (end of abstract) Agent: Kathy Manke Avago Technologies Limited - Fort Collins, CO, US Inventors: Kheng Leng Tan, Janet Bee Yin Chua, Kee Yean Ng USPTO Applicaton #: 20070295968 - Class: 257 79 (USPTO) The Patent Description & Claims data below is from USPTO Patent Application 20070295968. Brief Patent Description - Full Patent Description - Patent Application Claims
BACKGROUND OF THE INVENTION [0001]Light emitting diodes ("LEDs") are, in general, miniature semiconductor devices that employ a form of electroluminescence resulting from the electronic excitation of a semiconductor material to produce visible light. Initially, the use of these devices was limited mainly to display functions on electronic appliances and the colors emitted were red and green. As the technology has improved, LEDs have become more powerful and available in a wide spectrum of colors. [0002]With the fabrication of the first blue LED in the early 1990's, emitting light at the opposite end of the visible light spectrum from red, the possibility of creating virtually any color of light was opened up. With the capability to produce the primary colors, red, green, and blue (i.e., the RGB color model), with LED devices, there is now the capability to produce virtually any color of light, including white light. With the capability of producing white light, there is now the possibility of using LEDs for illumination in place of incandescent and fluorescent lamps, including use in outdoor lighting applications. The advantages of using LEDs for illumination is that they are far more efficient than conventional lighting, are rugged and very compact, and can last much longer than incandescent or fluorescent light bulbs or lamps. [0003]White light can be made in different ways: by mixing reds, greens, and blues; by using an ultraviolet ("UV") LED to stimulate a white phosphor; or by using a blue-emitting diode that excites a yellow-emitting phosphor embedded in an epoxy dome, where the combination of blue and yellow makes a white-emitting LED. Also, by combining a white phosphor LED with multiple amber LEDs, a range of different whites can be created. [0004]In a typical configuration, an LED may be positioned in a concave base cavity adapted to provide an initial focus for the light output from the LED. The LED may be provided with anode and cathode bonding wires communicating with conductive leads that place the LED in communication with an electrical circuit for supplying a bias voltage to the LED. LEDs are typically encapsulated in an optically clear epoxy resin material intended to protect the LED from external contaminants and from being physically damaged or dislodged during assembly and use, to provide mechanical support and thermal management, and sometimes to form part of a lens system for further focusing the light output of the LED. Epoxy resins are often selected as the encapsulant because of their material properties, including hardness, resistance to chemicals, good adhesion to diverse materials, and optical properties. [0005]However, along with light output, LED devices also generate heat. Despite typical design features of LED devices, including those summarized above, LED devices are commonly prone to damage caused by the buildup of heat generated from within the devices, as well as heat from sunlight in the case of outside lighting applications. Although metallized LED substrates are useful design elements that can be incorporated in LED devices and can serve to dissipate heat, these elements are often inadequate to maintain reasonably moderate temperatures in the devices. Excessive heat buildup can nevertheless cause deterioration of the materials used in the LED devices, such as encapsulants for the LED. Epoxy and silicone polymers, commonly used in LED encapsulant formulations, generally are poor heat conductors and are not sufficiently resistant to the high temperatures that often are generated inside LED devices during operation. These polymers can develop substantially reduced light transmissivity as they undergo heat degradation caused by such high temperatures. This reduced light transmissivity can increase absorbance by the LED devices themselves of light at wavelengths that are intended to be included in light output from the devices. This light absorbance may be more pronounced at near-ultra-violet wavelengths, and can cause commensurate declines in light output quality and intensity from an LED device. [0006]Moreover, in the case of white light diodes that generate emission by utilizing broad-spectrum phosphors that are optically excited by near-violet or UV radiation, there may be even faster degradation of the packaging materials, i.e., the epoxy around the diode used to encapsulate the light emitting device, due to the high photon energy that can cause chemical-bond cracks and a structural breakdown of the epoxy material. This results in luminance ("Lv") degradation, that is, less light output, over time as the phosphor/epoxy material is subjected to the UV radiation from the UV LED. [0007]One approach to improve the heat dissipation properties of LEDs is through the use of silicone as the encapsulant. Silicone (or more accurately, a "polysiloxane co-polymer") is both heat- and UV-stable and has a refractive index range from 1.38 to 1.60. Ideally, the refractive index of the encapsulant will be close to that of the semiconductor. However, the refractive index of a semiconductor in an LED is usually approximately 2.5. Consequently, there is reduction in the maximum light that can be extracted from the semiconductor. [0008]Epoxy with added antioxidants and UV inhibitors may also be used to minimize the UV effects on yellowing, both from sunlight heat and specific UV wavelengths. Although these antioxidants and UV inhibitors have a better refractive index than that of silicone and reduce yellowing, their effectiveness may be reduced over time, leaving the encapsulant susceptible to damage from sunlight and specific UV wavelengths. [0009]Consequently, there is a continuing need to provide new encapsulants for use in electroluminescent devices that have a better capability to dissipate heat and resist UV radiation in order to protect against degradation of the elements of the device. SUMMARY [0010]An encapsulant for use in electroluminescent devices containing light sources, which may include LEDs, that has improved heat-resistant and UV-resistant properties, is disclosed. The encapsulant may include nanoparticles suspended in an epoxy resin or a silicone polymer, where the nanoparticles are in a range of 5-165 nanometers ("nm") in diameter. The nanoparticles may be selected from groups of either oxides or non-oxides, where the oxides include silica (SiO.sub.2), titania (TiO.sub.2), alumina (Al.sub.2O.sub.3), zirconia (ZrO.sub.2), etc., and the non-oxides contain pure metals or metal borides, carbides and nitrides, such as titanium and its combinations (Ti, TiB.sub.2, TiC, and TiN). The nanoparticles may be present in a concentration less than 1.0% of the silicone matrix. [0011]In an example implementation, the selected nanoparticles may be suspended in the encapsulant, which may then be utilized in the electroluminescent device in various forms to cover a light source, including the encapsulant being applied in a concave base cavity or throughout the entire package where a dome or shell covers the package. The encapsulant may also be applied in the form of conformal coatings that may be applied over the light source in thin layers. A method of producing such an electroluminescent device is also disclosed. [0012]Other systems, methods and features of the invention will be or will become apparent to one with skill in the art upon examination of the following figures and detailed description. It is intended that all such additional systems, methods, features and advantages be included within this description, be within the scope of the invention, and be protected by the accompanying claims. BRIEF DESCRIPTION OF THE DRAWINGS [0013]The invention can be better understood with reference to the following figures. The components in the figures are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention. In the figures, like reference numerals designate corresponding parts throughout the different views. [0014]FIG. 1 shows a cross-sectional side view illustrating an example of an implementation of an electroluminescent device utilizing an LED as a light source (an "LED device") having an encapsulant containing nanoparticles filling a concave base cavity in which an LED is attached. [0015]FIG. 2 shows a cross-sectional side view illustrating another example of an implementation of an LED device having a dome covering an LED attached to a concave base cavity where the dome is filled with an encapsulant containing nanoparticles. [0016]FIG. 3 shows a cross-sectional side view illustrating another example of an implementation of an LED device having a dome covering an LED attached to a substrate where the dome is filled with an encapsulant containing nanoparticles. [0017]FIG. 4 shows a cross-sectional side view illustrating an example of an LED device that includes lead frames and a reflector cup wherein an encapsulant containing nanoparticles is applied to the reflector cup. [0018]FIG. 5 shows a cross-sectional side view illustrating another example of an implementation of an LED device having a shell covering an LED attached to a substrate where the shell is filled with an encapsulant containing nanoparticles. [0019]FIG. 6 shows a cross-sectional side view illustrating yet another example of an LED device that has lead frames and a reflector cup. [0020]FIG. 7 shows a cross-sectional side view illustrating an example of an implementation of an LED device having a conformal coating containing nanoparticles applied to the inner surface of a concave base cavity in which an LED is attached. [0021]FIG. 8 shows a cross-sectional side view illustrating an example of an implementation of an LED device that includes a conformal coating containing nanoparticles applied to the inner surface of a reflector cup. Continue reading... Full patent description for Electroluminescent device with high refractive index and uv-resistant encapsulant Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Electroluminescent device with high refractive index and uv-resistant encapsulant patent application. Patent Applications in related categories: 20080149942 - Iii-nitride light emitting device with reduced strain light emitting layer - In accordance with embodiments of the invention, strain is reduced in the light emitting layer of a III-nitride device by including a strain-relieved layer in the device. The surface on which the strain-relieved layer is grown is configured such that strain-relieved layer can expand laterally and at least partially relax. ... ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. Each week you receive an email with patent applications related to your keywords. Start now! - Receive info on patent apps like Electroluminescent device with high refractive index and uv-resistant encapsulant or other areas of interest. ### Previous Patent Application: Base apparatus of a light emitting diode and method for manufacturing the light emitting diode Next Patent Application: Led device having a top surface heat dissipator Industry Class: Active solid-state devices (e.g., transistors, solid-state diodes) ### FreshPatents.com Support Thank you for viewing the Electroluminescent device with high refractive index and uv-resistant encapsulant patent info. IP-related news and info Results in 2.21725 seconds Other interesting Feshpatents.com categories: Tyco , Unilever , Warner-lambert , 3m |
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